PDF Annotations Load/Remove

This pull request contains the load and remove annotation features that were missing from the last pull request. As well as some small CSS issues were fixed with the viewer. Overall the PDF viewer and annotations should be working now.

I also added a warning message when there is no selection box and the new annotation button is clicked. I added the key `select_an_area_pdf` to the `locales` language files. But for the languages that were not English I had to use Google translate. So someone might want to quickly review the wording if possible.
Rather than this comment here, I would prefer to move it up to the docstring.